U2A. ON-SITE UREA TO AMMONIA GENERATION: A COST EFFECTIVE, SAFE AND RELIABLE SOURCE OF AMMONIA FOR NO{sub}x CONTROL

摘要

The demand for highly efficient NO{sub}x control methodologies, such as Selective Catalytic Reduction (SCR) and Selective Non-catalytic Reduction (SNCR) technologies, have resulted in an increase in ammonia consumption. Between the two reductants used in commercial installations, namely Ammonia and Urea, the first is essential for most SCR applications. Notwithstanding, it presents serious environmental and operating risk, due to its high volatility and noxious nature. The Urea to Ammonia (U2A) Process is specially designed to offer a safe and benign alternative for obtaining ammonia from urea, as and when required, and therefore eliminates the necessity of storing large quantities of ammonia on-site. Historically, utilities seeking to install SCR systems have a choice between anhydrous or purely liquefied ammonia, and aqueous ammonia as the source of ammonia for injection into the SCR units. Anhydrous ammonia is highly toxic and is subjected to strict regulations. This, coupled with the fact that significant reserves are required for large stationary boilers, impose potential risks in the event of a spill. Aqueous ammonia poses similar risks, although less severe. For large boilers, however, the use of aqueous ammonia, results in huge energy consumption. Furthermore, decreasing the concentration of the solution in order to reduce the risks leads to a significant increase of transportation costs. All these factors make this source of ammonia economically unattractive. The use of Urea, a non-toxic and non-hazardous chemical, for most SCR applications was not possible until the introduction of U2A, a reliable technology for on-site ammonia generation.